Geosynthetic Systems Research Articles

Effectiveness of Hybrid Geosynthetic Systems in Controlling Differential Heave in Flexible Pavements over Expansive Soils

The challenge of maintaining ride quality and serviceability in flexible pavements built over expansive soil deposits remains a critical concern for transportation agencies. These expansive subgrades exhibit swell-shrink behavior in response to moisture fluctuations, leading to differential heaving and subsequent costly maintenance. This paper explores the effectiveness of a Hybrid Geosynthetic Reinforcement System (HGRS)—a composite of geocell and geogrid—as a targeted mitigation strategy for differential heaving induced by expansive soils. A large-scale box test was designed to simulate a flexible pavement section, consisting solely of a base course layer and the underlying expansive subgrade. Four test conditions were investigated: an unreinforced control, a geocell-reinforced section, a geogrid-reinforced section, and an HGRS-reinforced section. Vertical displacements on the surface of the base course layer were longitudinally monitored and compared against the control. The results reveal that the use of geosynthetic reinforcements, and HGRS in particular, significantly mitigates both maximum surficial heave and differential swelling. Among the systems tested, flexible pavements featuring HGRS demonstrated the most effective performance in alleviating the challenges posed by expansive soil deposits.

FBG Monitoring of a Communication Paths and Roadways with a Geosynthetic Systems on Mining Heaps

Abstract In civil engineering geosynthetics play the role of reinforcing the ground and strengthening the foundation structures of engineering facilities. This paper shows the possibility of using a geotextile, a geonet and a geogrid for the design of walking, cycle and quad-bike paths in the investigated mine waste dump sites. The functions of the solutions designed for linear investments in areas affected by mining activity and rehabilitated into a sports and recreation area must be monitored. The paper discusses the scope and the method of FBG monitoring, the data of which illustrate the behaviour of structures with embedded geosynthetic materials with regard to variables such as the structure service life and durability and the need to meet all limit states. The impact of the choice of designs with geosynthetics in sustainable development can be quantified in terms of the carbon footprint. A site-rehabilitation working design can also be analysed economically by estimating the market, investment and replacement values of a construction investment. In addition to key technical aspects, the discussed solutions in anthropogenic areas also ensure significant sustainable development of the Benefits system.

Adhesive Property and Road Performance Evaluation of Asphalt Overlay Pavement with Geotextile Interlayer

Geosynthetic interlayer systems are effective techniques to control reflective cracking and have better waterproof performance in damaged asphalt pavements. The interlayer bonding performance is critical to its function. This research investigated the interfacial adhesive property and road performance of asphalt overlay with geotextile interlayer. First, shear damage energy characteristics of geotextile interlayer have been investigated by varying tack coat types (SBS-modified asphalt, virgin asphalt, and emulsified asphalt), application rates (0.3 kg/m2–1.2 kg/m2), spraying times (1–2), upper mixture paving temperature (140°C–180°C), service temperature (5°C–45°C), and soaking time (0 h–96 h). In addition, bending fatigue tests, rutting tests, and semicircular bending tests were carried out to evaluate the comprehensive road performance of the asphalt overlay. The results showed that the interface adhesive property of asphalt overlay with geotextile interlayer using SBS-modified asphalt is best when the application rate is 0.8 kg/m2. The higher paving temperature is beneficial for the geotextile interlayer adhesion performance when the SBS-modified asphalt is sprayed at one time, while the paving temperature has almost no effect when the SBS-modified asphalt is sprayed at two times. The geotextile interlayer adhesion performance is less affected by temperature and more affected by water immersion. Compared with the common asphalt overlay types, the asphalt overlay with geotextile interlayer using SBS-modified asphalt shows better overall performance.

A simplified model for the analysis of piled embankments considering arching and subsoil consolidation

An analytical model is presented for the design of geosynthetic-reinforced and pile-supported (GRPS) embankments in this paper. The originality of the proposed solution lies in the fact that it allows considering the influence of the subsoil consolidation on the soil arching and geosynthetic strain. A nonlinear function is implemented to describe the subsoil behavior with the consolidation process in a closed-form solution. A simplified approach is then presented to link the arching development with the subsoil consolidation. The arching theory is combined with the tensioned membrane theory and the soil-structure interaction mechanisms to provide a simple and suitable design approach that enables a realistic approximation for designing soil–geosynthetic systems. The analytical model is capable of performing an ultimate and serviceability limit state design of GRPS embankments. While current methods cannot fully address the important effects of the subsoil consolidation, the analytical results suggested that arching and differential settlements increase with an increase of the subsoil consolidation degree. The analytical model is compared to field measurements and five other design standards for several full-scale field tests to study its validity. The results showed a satisfactory agreement between the proposed model and measured data, and generally better results are obtained as compared with other design methods.

Geosynthetic barrier systems used in dams, ponds, and reservoirs of Turkey

Geosynthetic barrier systems used in dams, ponds, and reservoirs of Turkey

Behaviour of piled embankment with multi-interaction arching model

The main focus of this paper is to present a multi-interaction model under a simplified form for calculating load transfer to piles and geosynthetic strain of piled embankments. The multi-interaction model is established by considering the integrated load transfer mechanisms and all the interactions between the elements of a geosynthetic-reinforced and pile-supported embankment, including fill soils, geosynthetic, platform, subsoil and pile. The proposed method is based on the combination of the tensioned membrane theory for geosynthetics, soil arching theory for fill soils, friction interaction model and, subsoil support. Thereby it allows providing a suitable design approach that enables a realistic and suitable approximation in designing soil–geosynthetic systems. The proposed method can be applied to both cohesive and non-cohesive fill soils. Using this method, the influence of the subsoil consolidation degree, subsoil ultimate bearing capacity, fill shear strength and platform, are investigated considering the behaviour and deformation of piled embankments. The result of the proposed method is compared to field measurements and to five other design standards to study its validity. The results showed a good agreement between the proposed method with measured data and are better than other design methods as well as two international design standards EBGEO and BS8006.

Influence of Reinforcement Fiberglass Grids Used in Asphalt Pavement on the Bonding of Layers

The paper deals with the influence of geosynthetic reinforcement systems on the quality of asphalt bonding layers. A reinforcing element in the form of a fiberglass grid is incorporated into the road structure between two asphalt layers to prevent the formation of cracks and to reduce the tendency of their subsequent propagation throughout the asphalt layers. At the same time, however, they form a potential weak interlayer on which adjacent asphalt layers may slip. The total 90 drilled cores taken from a laboratory-produced two-layer slabs were subjected to the Leutner shear test. The selection of individual specimens took into account both the type of reinforcement element and the amount of applied bituminous emulsion.

Stiffness of Soil-Geosynthetic Composite under Small Displacements. II: Experimental Evaluation

While most soil–geosynthetic interaction models have focused on the characterization of failure conditions, little emphasis has been placed on models and parameters suitable for characterizing the stiffness of soil–geosynthetic systems. In the companion paper, a soil–geosynthetic interaction parameter (KSGC) was developed that captures the stiffness of a soil–geosynthetic composite under small displacements. This included validation of the suitability of the assumptions and outcomes of the model for a specific set of materials and testing conditions. This paper presents the results of a comprehensive experimental program that allows the suitability of the model to be generalized for a wider range of materials and testing conditions. An initial test series was conducted using large-scale soil–geosynthetic interaction test equipment to evaluate the repeatability of the experimental results. A comparison of the test results from this series, as well as an assessment of an extensive database on the expected variability of soil and geosynthetic properties, revealed that the coefficient of variation of the model parameters was acceptable and well within the typical range of similar geotechnical and geosynthetic properties. Results from additional test series confirmed the linearity and uniqueness of the relationship between the geosynthetic unit tension squared and corresponding displacements, which are the key features of the proposed model. These tests were conducted under various conditions using different geosynthetic and backfill materials. Results also showed that the constitutive relationships adopted in the model were adequate for the extended range of confining pressures, geosynthetic lengths, geosynthetic types, and backfill soil types adopted in the study. The consistency of the results obtained in the experimental testing program underscores the suitability of the proposed KSGC parameter as a basis for the evaluation of soil–geosynthetic interactions under small displacements.

Centrifuge study of anchored geosynthetic slopes

ABSTRACT: This paper presents the results of centrifuge model testing on slopes reinforced by anchored geosynthetics and subjected to seepage conditions. The tests were conducted on 2V:1H slope models under steady seepage condition at 50g. Surface settlements and pore water pressures at different locations were recorded during the test. The influence of anchor stiffness, anchor length, and anchor pretensioning were examined. With an increase in anchor strength or stiffness, a considerable decrease in crest settlements and face movements was observed. Further, pretensioning of strands was found to be effective in enhancing the efficiency of anchored geosynthetic systems. Limit equilibrium stability analyses were in good agreement with the experimental results of slope models at failure.

Stability of geomembrane surface barrier of earth dam considering strain-softening characteristic of geosynthetic interface

Geosynthetic interfaces are characterized by strain-softening behaviors that exhibit a reduction in shear stress at relative shear displacements beyond peak strengths. The traditional practice in assessing the stability of geosynthetic barrier systems is based on Limit Equilibrium Method (LEM) which cannot consider the strain-softening behavior of interfaces. The safety factors calculated by LEM may overestimate the stability of geosynthetic barrier systems. A method combining LEM with numerical analysis for evaluating stability of geomembrane surface barrier of earth dam was proposed in this paper. The formula of calculating the factor of safety for geomembrane barrier systems taking account of the effect of interface strain-softening was derived. An example of composite geomembrane lined earth dam was numerically analyzed to verify the developed method. The calculated factor of safety is between the results that calculated from LEM using peak shear strength and residual shear strength. Through comparatively analysis with LEM results, it is suggested to use peak shear strengths along the basal interface and residual shear strength along the side slope interface in evaluating stability of geomembrane surface barrier of earth dam using LEM.

Centrifuge model studies on anchored geosynthetic slopes for coastal shore protection

This paper evaluates performance of anchored geosynthetic systems (AGS) on stability of slopes under seepage condition using a centrifuge modeling technique. A series of centrifuge tests were carried out at 50 g on unreinforced and AGS slope models, using a centrifuge container equipped with seepage flow simulator. AGS slope models were tested by varying slope inclination, number of anchors and keeping inclination of anchors as constant. The water was allowed to seep through the model slopes during flight at 50 g. Ground anchors were modeled as drilled pre-tensioned anchors using sand epoxy mixture, polyester strand and a plastic tube. An anchor inclination of 15° with the horizontal was adopted for AGS slopes. A layer of geocomposite was used for modeling geosynthetic component of anchored geosynthetic systems. All models were instrumented to measure surface settlements and pore water pressure within the slope at onset of seepage during centrifuge test. A digital image analysis technique was adopted to trace displacement vectors of plastic markers embedded toward the front elevation of the model and plastic markers glued to facing during model construction. Analysis and interpretation of centrifuge model test results indicate that the stability and deformation behavior of slopes, under seepage conditions, can be substantially improved using anchored geosynthetic systems. With an increase in slope inclination and reduction in number of anchors, surface settlements and face movements were observed to increase substantially. Further, stability analysis results on the unreinforced and AGS slope models were found to be in good agreement with those of physically observed centrifuge test results.

Discussion of “Modification to Translational Failure Analysis of Landfills Incorporating Seismicity” by Xuede Qian and Robert M. Koerner

Discussion of “Modification to Translational Failure Analysis of Landfills Incorporating Seismicity” by Xuede Qian and Robert M. Koerner

Enhanced Measurement of Geosynthetic Interface Shear Strength Using a Modified Inclined Plane Device

Abstract Composite lining systems comprising different geosynthetics and soil are typical capping devices in modern landfills. Analyses of the behavior of capping devices have shown that they are very sensitive components thanks in part to the shear strength of geosynthetic interfaces, many of which were reported to have controlled slippage between capping lining components during landfill slope failures. There are some laboratory testing alternatives for measuring the shear strength of the interface between geosynthetics or between geosynthetics and soil. The inclined plane test is especially appropriate for shear strength tests under low normal pressure which is a specific condition of these geosynthetic systems on cap cover. However, the selected shear strengths, inferred from the laboratory experimentation, show considerable variability, which depends on the test procedure. This work proposes a new procedure and a new interpretation of the inclined plane test taking as an example the interface between geospacers and geomembranes often considered as a critical interface. The measurement of displacement acceleration during the test gives the possibility of more accurately defining the large sliding displacement shear strength, which may approach the true residual condition.

Model study of sandy slopes under uniform seepage and reinforced with anchored geosynthetics

ABSTRACT: The stability of soil slopes can be significantly increased as a result of the in situ stabilization technique of anchored geosynthetic systems (AGS). An experimental study was performed on AGS sandy slope models with different cross-sections and subjected to uniform seepage. The slope models were brought to failure by gradually decreasing the AGS loads. A comparative analysis of the failed models in terms of the predicted safety factors and slip surface configurations were carried out using limit equilibrium and finite element analyses. Good agreements were obtained between the experimental and theoretical predictions in terms of the failure surface configurations as well as the safety factor at failure. Surface load applications on homogenous, granular slopes tend to change the failure mode from a planar slide assumed by the infinite slope theory to a more rotational sliding.

State-space solution of seabed–geotextile systems subjected to cyclic wave loadings

Analytical solutions for dynamic responses of seabed–geotextile systems subjected to cyclic wave loadings are presented in this paper, which contains the solutions of the transient and harmonic responses. The theory is based on the Biot consolidation equations in which the pore fluid as well as the soil skeleton is considered compressible and the flow in the porous seabed is assumed governed by Darcy's law. The present analysis is completely based on the state-space formulations, which is very effective for laminated systems analysis. Together with Laplace–Fourier transform techniques, state-space methods are used to solve the governing equations. Responses of seabed–geotextile systems can be calculated by using the matrix theory, boundary conditions and inverting integral transform. As illustrative examples, laboratory experiments, which conducted at the Oregon State University Wave Research Facility in USA by McDougal [1981. Ocean wave–soil–geotextile interaction. Ph.D. Dissertation, Oregon State University], are analysed. It is shown that the numerical results are in good agreement with those obtained from laboratory experiments, and the distinction between the transient and harmonic response should be taken into account for design of marine geosynthetic systems. Under the transient condition, the seabed is apt to liquefy. Seabed stability may be increased by placing geotextile beneath an armour layer. The numerical evaluations of the solution in the seabed–geotextile systems can be easily achieved with high efficiency and accuracy.

Quantifying hook and loop interaction in textured geomembrane–geotextile systems

This paper examines the role of geomembrane texture on geomembrane–geotextile interface performance, focusing in particular on hook and loop interaction. The study specifically involves textured HDPE geomembranes and needle punched nonwoven fabrics; however, the concepts presented may be relevant to other geosynthetic systems. The effects of hook and loop interaction on geosynthetic interface performance were quantified through laboratory interface shear testing, ASTM hook and loop interaction tests, and optical microscopy. Testing was conducted over a large range of normal stresses (0.4–312 kPa) to capture variations in behavior as a function of normal stress. Results show that the magnitude of hook and loop interaction depends on the characteristics of the geomembrane texture and can contribute a significant portion of the peak interface strength. The results aid in quantifying behavioral differences observed between geomembranes textured using different manufacturing processes, and provide microscale insight into textured geomembrane–geotextile interaction mechanisms over a range of stress levels.

Application of Anchored Geosynthetic Systems for In Situ Slope Stabilization of Fine-Grained Soils

The use of anchored geosynthetic systems (AGS) was proposed by Koerner et al. for the stabilization of slopes at or near their failure state. AGS provides in-situ stabilization of soil slopes by combining a surface-deployed geosynthetic with an anchoring system of driven reinforcing rods similar to soil nailing. Installation of the system involves tensioning a geosynthetic over a slope’s surface by driving anchors through the geosynthetic at a given spacing and distance. By tensioning the geosynthetic over the slope’s surface, a compressive load is applied to the slope. Benefits of AGS are described to include the following: ( a) increased soil strength due to soil compression, including increased compressive loading on potential failure surfaces; ( b) soil reinforcement through soil nailing; ( c) halt of soil creep; ( d) erosion control; and ( e) long-term soil consolidation. Following installation of the AGS and 1 year of monitoring, it was found that the anchored geosynthetic system provided only some of the reported benefits and in general did not function as an active stabilization system. This was in part because the system could not provide and maintain loading on the geosynthetic. The geosynthetic, however, did tension when slope movement occurred, preventing the slope from failing. Thus, the system functioned more as a passive restraint system and appeared to function well over the monitoring period.

Stabilization of Coastal Slopes by Anchored Geosynthetic Systems

Coastal slopes are subjected to destabilizing forces from wave action, current scour, and exfiltrating ground water. As such, they are vulnerable to both surficial erosion and shallow sliding failure because of their low shear strength near the surface. One way of increasing the stability of these slopes is to increase the confining stress on the ground surface by means of an anchored geosynthetic system (AGS). This approach is less visually and physically intrusive than traditional “hard armor” methods, which in many instances are prohibited in environmentally sensitive areas such as coastal sand dunes. Theoretical relationships for determining required AGS loads and anchorage lengths are presented that can be used to evaluate stability for different soil conditions and seepage directions. Some important variables affecting AGS performance such as failure depth, surface configuration, anchor orientation, and seepage influence on near-surface stability are also described. The theoretical predictions were examined by conducting laboratory stability tests on saturated sand slopes, which were stabilized by an anchored geosynthetic netting and subjected to parallel seepage and tractive surface stresses. Good agreement was observed between predicted and actual anchor loads at failure.

Remediation of existing canal linings

The Bureau of Reclamation (Reclamation) has installed over 4,000,000 m 2 of geomembrane canal liner since 1968. Reclamation continues to evaluate the performance of new materials in new applications for canal lining. Recent installations in South Dakota, Washington, Nebraska and Oklahoma contain relatively new materials installed as either exposed or covered canal liners. Although the majority of geomembranes used as canal liners have been soil covered, since July of 1987, several geosynthetic systems have been covered with concrete or left exposed. Results from monitoring a soil covered polypropylene (PP) geomembrane in South Dakota, an exposed high density polyethylene (HDPE) geomembrane in Kansas, and an exposed very low density polyethylene (VLDPE) geomembrane in Nebraska are reported in this paper. Geomembranes used as canal liners appear to reduce seepage in the canals when they are constructed in highly permeable or collapsible types of soils.

Design of anchored geosynthetic systems for slope stabilisation : Hryciw, R D; Haji-Ahmad, K Proc Conference Stability and Performance of Slopes and Embankments II, Berkeley, 29 June–1 July 1992V2, P1464–1480. Publ New York: ASCE, 1992 (ASCE Special Geotechnical Publication No 31)

Design of anchored geosynthetic systems for slope stabilisation : Hryciw, R D; Haji-Ahmad, K Proc Conference Stability and Performance of Slopes and Embankments II, Berkeley, 29 June–1 July 1992V2, P1464–1480. Publ New York: ASCE, 1992 (ASCE Special Geotechnical Publication No 31)